Dolby Laboratories DP564 - Manual (Page 79)

DP564 Multichannel Audio Decoder Appendix A: Metadata
A-9
• Music Standard
Max Boost: 12 dB (below –55 dB)
Boost Range: –55 dB to –31 dB (2:1 ratio)
Null Band Width: 5 dB (–31 dB to –26 dB)
Early Cut Range: –26 dB to –16 dB (2:1 ratio)
Cut Range: –16 dB to +4 dB (20:1 ratio)
• Speech
Max Boost: 15 dB (below –50 dB)
Boost Range: –50 dB to –31 dB (5:1 ratio)
Null Band Width: 5 dB (–31 dB to –26 dB)
Early Cut Range: –26 dB to –16 dB (2:1 ratio)
Cut Range: –16 dB to +4 dB (20:1 ratio)
• None
No DRC profile selected. The dialogue level parameter (dialnorm) is still applied.
These choices are available to the content producer for both Line Mode and RF
Mode. The content producer chooses which of these profiles to assign to each mode;
when the consumer or decoder selects a DRC mode, the profile chosen by the
producer is applied.
In addition to the DRC profile, metadata can limit signal peaks to prevent clipping
during downmixing. This metadata, known as overload protection, is inserted by the
encoder only if necessary. For example, consider a 5.1-channel program with signals
at digital full scale on all channels being played through a stereo, downmixed line-
level output. Without some form of attenuation or limiting the output signal would
obviously clip. Correct setting of the dialogue level and DRC profiles normally
prevents clipping and unnecessary application of overload protection.
Note: DRC profile settings are dependent on an accurate dialogue level setting.
Improper setting of the dialogue level parameter may result in excessive and
audible application of overload protection.
A.4 Downmixing
Downmixing is a function of Dolby Digital that allows a multichannel program to be
reproduced over fewer speaker channels than for which the program is optimally
intended. Simply put, downmixing allows consumers to enjoy a DVD or digital
television broadcast without requiring a full-blown home theater setup.
As with stereo mixing where the mix is monitored in mono on occasion to maintain
compatibility, multichannel audio mixing requires the engineer to reference the mix
to fewer speaker channels to ensure compatibility in downmixing situations. In this
way, Dolby Digital, using the metadata parameters that control downmixing, is an
“equal opportunity technology” in that every consumer who receives the Dolby
Digital data stream can enjoy the best audio reproduction possible, regardless of the
playback system.